Generally, a radio frequency (RF) multiplier is an electronic circuit that generates an output signal whose output frequency is a harmonic of its input frequency. A harmonic is a wave with a frequency that is a positive integer multiple of the frequency of the original wave, known as the fundamental frequency. Frequency multipliers typically include a nonlinear circuit that distorts an input signal and generates harmonics of the input signal. A subsequent bandpass filter typically selects the desired harmonic frequency and removes the unwanted fundamental and other harmonics from the output. The original wave may also be called the first harmonic, and the following harmonics may be referred to as higher harmonics. As all harmonics are periodic at the fundamental frequency, the sum of harmonics is also periodic at that frequency.
One exemplary active RF multiplier is a Gilbert cell-based active frequency doubler which typically utilizes bipolar transistors to operate as a precision multiplier and is typically used in modern communication systems as a multiplier and frequency translator. The Gilbert cell-based active frequency doubler typically utilizes the multiplier circuit to drive an RF port and a local oscillator (LO) port from the same input terminal. The multiplier circuit of the Gilbert cell-based active frequency doubler typically stacks two layers of transistors and current sources, and, therefore, typically requires a high supply voltage in order to suitably operate. Further, the transconductor inputs are typically tied to the fundamental RF signal that also drives the switching core of the Gilbert cell-based active frequency doubler which degrades overall conversion efficiency of the Gilbert cell-based active frequency doubler. Another drawback of Gilbert cell-based active frequency doublers is that the outputs of the Gilbert cell-based active frequency doublers are not adequate in strength to drive RF mixers directly. That is, an amplifier is typically added to the system to drive the RF mixers. Another drawback of Gilbert cell-based active frequency doublers is that they typically do not have sufficient output power to drive cascaded doublers, which typically double the fundamental RF frequency, to make quadruplers, which typically quadruple the fundamental RF frequency. Another drawback of Gilbert cell-based active frequency doublers is excessive degradation of fundamental suppression due to transistor device offset voltages.